When providing a call service, a portable electronic device can output a voice signal of a called party at a predetermined volume. If a surrounding noise of the portable electronic device is severe, there can be a problem that, because the surrounding noise masks an output signal of the portable electronic device, a user of the portable electronic device cannot recognize the output signal.
To solve the problem that the output signal is masked by the surrounding noise, the portable electronic device can provide an automatic volume adjustment service based on the surrounding noise. For example, when an audio signal is input through a microphone, the portable electronic device can identify a level of a surrounding noise included in the audio signal. And then, the portable electronic device can automatically set a volume of an output signal according to the level of the sounding noise.
However, because howling in which a signal output from a speaker flows into the microphone is recognized as a surrounding noise in the portable electronic device, when the portable electronic device provides the automatic volume adjustment service, there can be a problem that the howling brings about a continuous increase of the volume of the output signal.